1. Field of the Invention
The present invention relates to a data structure and a retrieval technology, for retrieving record such as an attribute information of contents data.
2. Related Art
There has conventionally been known a content decentrally saving system in which a plurality of contents data are decentrally saved in a plurality of node apparatus, which are communicable to each other through a network. In such a kind of content decentrally saving system, each of the node apparatus utilizes a content catalog information in which attribute information of the contents data are described. Each node apparatus may retrieve a predetermined contents data and acquire contents from the other node apparatus or a content management server. The attribute information includes information about a content name, an opening start time to the public, an opening ending time and a keyword for the contents data. Each attribute information is associated with an index information such as a content ID. The content catalog information is created by the content management server and delivered to respective node apparatus. In case where new contents data are added or utilization of the contents data is completed in the content decentrally saving system, the content catalog information is updated by the content management server. The content catalog information is delivered to respective node apparatus.
An increased number of available contents data in the content decentrally saving system results in an increased amount of data of the content catalog information. Accordingly, there has been a problem that the content catalog information cannot be stored in a single node apparatus. In order to solve this problem, there has been proposed a method in which a plurality of contents catalog information sections into which the content catalog information is divided, are decentrally stored in a plurality of node apparatus. In such a method, an assigned rage of the contents data is set for the respective node apparatus. The respective node apparatus stores the content catalog information in which attribute information of the contents data for the assigned range has been described. Here, the assigned range has been determined as a range of a content ID serving as the index information. Therefore, it is possible to narrow down, upon retrieving the attribute information with a retrieval key of the content ID, the node apparatus storing the content catalog information, in which the corresponding attribute information has been described, from the content ID.
However, if a retrieval is conducted with a retrieval key of the other information than the content ID, there is no clue to narrow down the information, with the result that a full retrieval of the content catalog information is required. In this case, much retrieval time is therefore required in comparison with a case where a retrieval is conducted with a retrieval key of the content ID.